Mac-Based Broadcast Domains; Ieee 802.1Q Vlans - D-Link DES-3624 Series User Manual

Stackable NWay Ethernet Switch User's Guide
setup on your network and configure the Switch accordingly. 802.1Q VLANs support IEEE 802.1Q tagging,
which enables them to span the entire network (assuming all switches on the network are IEEE 802.1Q-
compliant). In contrast, MAC-based broadcast domains are limited to the Switch and devices directly
connected to them.
All VLANs allow a network to be segmented in order to reduce the size of broadcast domains. All broadcast,
multicast, and unknown packets entering the Switch on a particular VLAN will only be forwarded to the
stations or ports (802.1Q and port-based) that are members of that VLAN. 802.1Q and port-based VLANs also
limit unicast packets to members of the VLAN, thus providing a degree of security to your network.
Another benefit of 802.1Q and port-based VLANs is that you can change the network topology without
physically moving stations or changing cable connections. Stations can be 'moved' to another VLAN and thus
communicate with its members and share its resources, simply by changing the port VLAN settings from one
VLAN (the sales VLAN, for example) to another VLAN (the marketing VLAN). This allows VLANs to
accommodate network moves, changes and additions with the utmost flexibility. MAC-based broadcast
domains, on the other hand, allow a station to be physically moved yet still belong to the same broadcast
domain without having to change and configuration settings.
The untagging feature of IEEE 802.1Q VLANs allows VLANs to work with legacy switches that don't
recognize VLAN tags in packet headers. The tagging feature allows VLANs to span multiple 802.1Q-
compliant switches through a single physical connection and allows Spanning Tree to be enabled on all ports
and work normally (BPDU packets are not tagged).

MAC-Based Broadcast Domains

The Switch supports up to 12 MAC-based broadcast domains, which are by their nature, limited to the Switch
itself and the devices connected directly to it.
Since MAC addresses are hard-wired into a station's network interface card (NIC), MAC-based broadcast
domains enable network managers to move a station to a different physical location on the network and have
that station automatically retain its broadcast domain membership. This provides the network with a high
degree of flexibility since even notebook PC's can plug into any available port on a network and communicate
with the same people and use the same resources that have been allocated to the broadcast domain in which
it is a member.
Since MAC-based broadcast domains do not restrict the transmission of known unicast frames to other
broadcast domains, they can only be used to define limited broadcast domains. As such, they are best
implemented on networks where stations are frequently moving, for example where people using notebook
PCs are constantly plugging into different parts of the network.
Setting up MAC-based broadcast domains is a relatively straightforward process. Simply create the broadcast
domain by assigning it a name (description) and add MAC addresses for the stations that will be members.

IEEE 802.1Q VLANs

The Switch supports up to 2000 802.1Q VLANs. 802.1Q VLANs limit traffic that flows into and out of switch
ports. Thus, all devices connected to a port are members of the VLAN(s) the port belongs to, whether there is
a single computer directly connected to a switch, or an entire department.
On 802.1Q VLANs, NICs do not need to be able to identify 802.1Q tags in packet headers. NICs send and
receive normal Ethernet packets. If the packet's destination lies on the same segment, communications take
place using normal Ethernet protocols. Even though this is always the case, when the destination for a packet
lies on another Switch port, VLAN considerations come into play to decide if the packet gets dropped by the
Switch or delivered.
Switch Management Concepts 37